Modelling of nuclear energy systems with MESSAGE

MESSAGE was originally developed at IIASA for its global energy studies [31]. The model was acquired by the IAEA and enhanced for supporting capacity building activities in Member States for energy and nuclear power planning [3]. It is basically a technology oriented, system engineering model that combines the technical, economic and environmental performance of different energy supply and use technologies and optimizes system-wide performance over the medium to long term. It has been extensively used at global, regional and national levels for developing scenarios to support energy planning and policy analysis.

MESSAGE-NES is an adapted and enhanced version of the model that has been used in various INPRO studies [32]. Based on experience with the model for INPRO studies under its major projects such as GAINS and SYNERGIES, MESSAGE-NES has been included in INPRO’s scenario analysis and decision support toolkit. It provides a convenient platform for modelling complex NESs and for developing alternative scenarios of the dynamic evolution of the system. It helps evaluate trade-offs between various aspects of sustainability of an NES. Figure 11 shows the MESSAGE representation of a simple energy system and of the details of an NES. Depending upon the scope of the study, the NES can be represented on an aggregated level or with full details of the associated nuclear fuel cycle.

MESSAGE-NES includes calculations of dynamic mass flows across the nuclear fuel cycle, including natural resource depletion, spent fuel and radioactive waste accumulation and specific material inventories. As for the comparison of alternatives, the user can define the selection criterion — the objective function. For example, it is possible to focus on economic performance by using cost minimization as the main criterion, to address environmental and public risks by using minimization of radioactive waste accumulation as the main criterion, or to consider non-proliferation concerns by minimization of inventories of critical materials like plutonium as the main criterion. It is also possible to combine various criteria by assigning weights to each of them and optimizing the overall system evolution.

The main outputs of the model include an optimized deployment plan for various nuclear technologies, including details of (a) the sizes and timings for building various facilities and services of an NES; (b) material mass flows, inventories, resource depletion and accumulated radioactive wastes;

and (c) investment and operating costs.

The main features and capabilities of MESSAGE-NES are documented in the MESSAGE-NES User Guide [32], which also provides detailed guidance on the modelling of specific technical and

economic aspects of various nuclear reactor technologies and their respective fuel cycle facilities. Three demonstration cases are also presented: (i) an NES based on once-through fuel cycle for LWRs and HWRs; (ii) an NES based on a partly closed fuel cycle for LWRs and HWRs, with recycling of recovered uranium and plutonium in the form of MOX fuel for LWRs; (iii) an NES based on a fully closed fuel FIG. 11. MESSAGE representation of (a) a simple energy system, including nuclear technology, and (b) nuclear power with details of the nuclear fuel cycle. Legend: cnLWR — conversion of uranium for LWR fuel; Coal-Ext — coal extraction;

Coal PP — coal-fired power plant; crLWR — dummy form needed to model discharged fuel transfers to and between storage; Dep U — depleted uranium; dummy — dummy back-stop technology; Elec_TD — electricity transmission and distribution; enLWR — enrichment of uranium for LWR fuel; fcLWR — auxiliary technology to put discharged LWR fuel into cooling storage; fuUOXLWR — uranium oxide fuel fabrication for LWR; ISFLWR — interim dry storage for LWR spent fuel; LWRUOX — LWR operating on uranium oxide fuel; Nat U — natural uranium; Oil_Imp — oil import; Oil_PP — oil power plant; Oil_P_S — oil processing and supply; Oil_S_F — oil secondary to final; SF — spent fuel; SFLWR — cooling storage for LWR spent fuel; SWLWR — separative work for LWR fuel; tsLWR transport of LWR spent fuel from cooling storage to ISFLWR.

cycle, with multiple recycling of plutonium from thermal and fast reactors. These cases can be used as the starting point for national experts to elaborate their own system level models of national NESs using MESSAGE-NES.

The application of MESSAGE-NES to a variety of country case studies is documented in Ref. [33].

For example, an Argentinian case study modelled an NES with a once-through fuel cycle and HWRs considering existing and possible future facilities. This case study explored the advantage of building local fuel cycle facilities and their optimal timings and sizes as nuclear electricity generation increases in future. The case study also determined the nuclear material requirements, inventories and waste accumulation. The representation of the Argentinian NES in MESSAGE-NES is shown in Fig. 12.

Another example of NES modelling in MESSAGE-NES is a case study of China for an NES based on thermal and fast reactors in a closed nuclear fuel cycle. The complex material flow in this system was represented in MESSAGE-NES, as shown in Fig. 13.

FIG. 12. MESSAGE-NES representation of the NES based on HWRs in the once-through nuclear fuel cycle from the Argentinian case study. Legend: ATU_1 —Atucha I NPP; ATU_2 —Atucha 2 NPP; CAREM —small modular reactor CAREM; DEP_U — depleted uranium; DIOXITEX_UO2_NAT — natural enrichment uranium dioxide from local supplier Dioxitek S.A.; DUMMY_n — dummy back-stop technology; EMB — Embalse NPP; FC_NPPn — fuel cycle for n-th NPP; IMP NAT_U — imported natural uranium; IMP UO2_3.5% — imported UO2 with 3.5% enrichment; IMP UO2_4.8% — imported UO2 with 4.8% enrichment; IS_NPPn — intermediate storage of spent fuel for n-th NPP; LOCAL ENRICH_3.5% — local enrichment 3.5%; MIX 3.1%, MIX 4.45%, MIX_LEU — different considered variants of fuel mix for different reactors (natural uranium is mixed with enriched uranium in certain proportions); NAT_U — natural uranium;

NF — nuclear fuel; NPP — nuclear power plant; PWR — pressurized water reractor; SF_NPPn — spent fuel n-th NPP;

SPENT FUEL_n — spent fuel of n-th NPP; SWU — separative work units; TS_NPPn — transport of spent fuel from cooling storage to intermediate dry storage; U_EXTR — uranium extraction; UF6_CONV — conversion to UF6; UF6_NAT — UF6 with uranium of natural enrichment; UO2_ x.y% — uranium dioxide fuel of x.y% enrichment; UO2_LEU — uranium dioxide fuel. based on low-enriched uranium.

4.3. COMPARATIVE EVALUATION OF NUCLEAR ENERGY SYSTEMS WITH KIND-ET